Got home from work to find a large envelope... opened it, and it's an image book from Sigma! The cover letter from Sigma UK says it is a gift to those who have registered multiple lenses with them. I presume it is a worldwide thing.

The book itself is mostly monochrome. Content mostly contains images of random bits of lens internals, shots of workers making the lenses, and also product shots featuring their "new" lenses (the S, A, C ones). There is no text in the book, other than a reference to sigma-global.com on the back.